This invention relates to printing presses in general and, in particular, to a multicolor, rotary printing press comprising a plurality of plate cylinders for printing as many different color images on a continuous web of paper. More particularly, the invention pertains to means in such a printing press for fine positional readjustment of each plate cylinder in both lateral (axial) and circumferential directions thereof for exact registration of the images with a reference image printed by one of the plate cylinders.
A variety of approaches have been made for printing in exact registration of multicolor images by a rotary printing press. Of such conventional efforts, one that is most pertinent to the instant invention is that disclosed in Japanese Unexamined Patent Publication No. 53-134507. The plate cylinder according to this prior art device is split into two halves along a plane at right angles with the cylinder axis, one of the cylinder halves being movable both laterally (axially) and circumferentially relative to the other. The split plate cylinder is provided, at each of its opposite ends, with a lateral adjustment and a circumferential adjustment whereby each cylinder half is positionally adjustable independently, even during printing.
Each lateral adjustment of the noted unexamined patent publication includes a screw-threaded rod which is coaxially and rotatably coupled to each lateral end of the plate cylinder while being restrained from lateral displacement relative to the same. The threaded rod is matingly engaged with an internally threaded sleeve which is rotatably mounted to the frame while being locked against lateral displacement relative to the same. Thus, as the threaded sleeve is driven bidirectionally, the threaded rod travels back and forth with one of the plate cylinder halves for readjustment of its lateral position.
Each circumferential adjustment, on the other hand, of the same prior art device includes another sleeve which is fitted over one end portion of the plate cylinder shaft for relative displacement in its lateral direction only. One end of the sleeve is coaxially joined to a helical gear which is in mesh with another such gear on the neighboring blanket cylinder. Also coupled to the sleeve is a spur gear which is rotatable relative to the sleeve but which is locked against lateral displacement relative to the same. This spur gear is coaxially provided with an externally threaded boss which is engaged with an internally threaded member mounted fast to the frame.
Therefore, on being driven angularly bidirectionally, the spur gear laterally travels back and forth with the sleeve on the plate cylinder shaft because of the mating engagement of its threaded boss with the fixed, internally threaded member. Traveling laterally, moreover, the sleeve is forced to make angular displacement with the plate cylinder shaft as the helical gear thereon slides in mating engagement with the similar gear on the blanket cylinder. The plate cylinder half is thus readjusted in its circumferential position.
Another similar register control device is found in Japanese Unexamined Patent Publication No. 63-91248. This second prior art device also has a sleeve which is formed in one piece with a helical gear for driving the plate cylinder and which is rotatably coupled to the plate cylinder shaft while being restrained from lateral displacement relative to the same. The sleeve is externally threaded for mating engagement with an internally threaded member affixed to the frame and carries on its end away from the helical gear a pinion in engagement with a rack for lateral adjustment.
The circumferential adjustment of this second prior art device has a second sleeve fitted over the first mentioned sleeve and screw-threadedly engaged therewith. The second sleeve has one end thereof rotatably coupled to the helical gear and restrained from lateral displacement relative to the same. The other end of the second sleeve is shaped into a pinion engaging with another rack for circumferential adjustment.
Both prior art devices are alike in having gears or toothed wheels driven by rotary or linear actuators. Mechanically farthest away from the plate cylinder shaft to be driven, these drive wheels are threadedly engaged with sleeves or the like in order to enable translation from rotary to linear motion. The linear motion is imparted more or less directly to the plate cylinder for its lateral displacement and, for circumferential displacement, reconverted into rotary motion by the relative sliding motion of the intermeshing helical gears through which the plate cylinder is driven during printing.
Typically, in offset rotary printing presses for newspaper production, the maximum allowable lateral displacement of the drive wheels for lateral adjustment is set in a range of four to six millimeters, and that of the drive wheels for circumferential adjustment in a range of twelve to eighteen millimeters. In practice, however, the drive wheels have often been driven in excess of these limits as the rotary or linear actuators are left in operation for prolonged periods of time due to some errors in control or in manual operation.
One frequent result of such overdriving has been the riding of the drive wheels onto the incomplete threads of the rods or the sleeves, with the consequent jamming of the adjustments. Some movable parts of the adjustments have also been easy to run into some other parts with which they should be totally out of contact, again resulting in jamming and, in the worst case, in the irreparable damage of these parts.
It has often been impossible to recover, for instance, the drive wheels back from the incomplete threads merely by reversing the actuators. Prolonged periods of time have thus had to be expended for recovery from such troubles, adding very substantially to the downtime, as well as the maintenance costs, of the multicolor printing press. Obviously, moreover, the useful life of the press must also have been considerably curtailed.
The present invention seeks totally to preclude the overrunning of both lateral and circumferential adjustments incorporated in a multicolor printing press for image registration purposes, thereby enhancing reliability in the operation of the adjustments, reducing the downtime of the machine, and extending its useful life.
Briefly, the invention may be summarized as an apparatus for fine positional adjustment of a plate cylinder in both lateral and circumferential directions thereof for image registration of a multicolor rotary printing press. Included is a plate cylinder supported by frame means for both lateral and circumferential displacement. Lateral adjustment means act between the plate cylinder and the frame means for positional adjustment of the plate cylinder in a lateral direction thereof relative to the frame means. Circumferential adjustment means also act between the plate cylinder and the frame means for positional adjustment of the plate cylinder in a circumferential direction thereof relative to the frame means.
The invention particularly features lateral overrun prevention means for limiting the bidirectional rotation of a first rotary member of the lateral adjustment means relative to the frame means in order to prevent the plate cylinder from being driven laterally beyond limits, and circumferential overrun prevention means for limiting the bidirectional rotation of a second rotary member of the circumferential adjustment means relative to the frame means in order to prevent the plate cylinder from being driven circumferentially beyond limits.
In a preferred embodiment both first and second rotary members take the form of driven gears, which are in mesh with drive pinions on the output shafts of lateral and circumferential drive motors, respectively. Locking the driven gears against rotation in the event of an emergency, rather than other rotary or movable parts of the lateral and the circumferential adjustment means, is preferred because the driven gears can be easily made large enough to be arrested lightly.
Adapted for this embodiment, the lateral overrun prevention means comprises a limit stop formed on the frame means, and a projection formed eccentrically on the driven gear of the lateral adjustment means for movement into abutment against the limit stop with the prolonged rotation of the driven gear. Preferably, normally positioned at an angular distance of approximately 180 degrees from the limit stop, the projection is to travel, with the bidirectional rotation of the driven gear, into possible abutment against the opposite sides of the limit stop.
The circumferential adjustment means likewise comprises limit stop means on the frame means, and projection means formed eccentrically on the driven gear of the circumferential adjustment means for movement into abutment against the limit stop with the prolonged rotation of the driven gear. Since the driven gear not only rotates but travels laterally for circumferential positioning of the plate cylinder, the limit stop means may have a pair of limit stops spaced from each other laterally of the driven gear. The projection means may have a pair of projections formed on opposite sides of the driven gear for movement, with the combined bidirectional rotary and lateral motion of the driven gear, into abutment against the respective limit stops.
Thus, with the driven gears of both lateral and circumferential adjustment means positively restrained from rotation beyond limits, no undue displacement of the plate cylinder is to take place in either its lateral or circumferential direction. Moreover, when either or both of the driven gears are locked against rotation by the overrun prevention means, no damaging force will be exerted on any parts of the adjustment means or on any associated parts of the press.
It is also preferred that both lateral and circumferential adjustment means include drive means such as rotary or linear actuators having their output forces optimally preadjusted in order to avoid damage upon functioning of the overrun prevention means. Stepper motors are particularly recommendable as they suffer no damage at all, mechanically or electrically, when forced to stop.
Altogether, the multicolor printing press built on the novel concepts of the invention will drastically reduce both downtime and operating hours per unit volume of production. These results will be of particular advantage in newspaper production which is hard pressed for time.
The above and other objects, features and advantages of the invention and the manner of realizing them will become more apparent, and the invention itself will best be understood, from the following description taken together with the attached drawings showing some preferred embodiments of the invention.